Seals used in bearings generally consist of a single structural element, typically an annular ring or disk that is fixed to one race with a sealing lip that rides on the other race. When a higher level of sealing integrity is desired, a seal with more than one sealing lip is necessary. One alternative is to mold a single seal with two or more lips. This complicates the molding process, because the multiple lips radially overlap one another, creating concavities or undercuts. Such a seal cannot be simply or easily molded because, as the molds part, the seal lips will have to be pulled forcefully past that part of the mold that forms the concavities between the lips.
Consequently, multiple seal lips are sometimes provided by stacking together a number of separate disks. Each disk in the stack provides one seal lip, and can be easily molded by itself. The drawback of a stacked seal, compared to a unitary multiple lip seal, is that each disk has to be handled separately at installation and oriented so that all the lips face the right way. Sometimes, the stack of disks or layers is crimped together in the proper orientation prior to installation by a separate casing, but that represents an additional component and manufacturing step.